Aspen (Populus tremula)

Present distribution

Scientific name:	Populus tremula L.
Common name(s):	Aspen

Map showing the present distribution of this weed.

Habitat:

Native to Europe, Asia and northern Africa, Aspen has a broad climatic range from within the arctic circle in Norway and the Scottish highlands to the drought ravaged Hungarian steppe to cliffs in Shetland, floodplains and peat bogs (Worrell 1995). Most commonly found in woodlands, it is harvested for timber in managed forests of Scandinavia and has been known to invade pasture through suckering if parent populations are nearby (Clapham, Tutin & Warburg 1952; Webb, Sykes & Garnock-Jones 1988; Worrell 1995)

Potential distribution

Potential distribution produced from CLIMATE modelling refined by applying suitable landuse and vegetation type overlays with CMA boundaries

Map Overlays Used

Land Use:
Forest private plantation; forest public plantation; pasture dryland; pasture irrigation

Broad vegetation types
Coastal scrubs and grassland; coastal grassy woodland; heathy woodland; lowland forest; heath; swamp scrub; box ironbark forest; inland slopes woodland; sedge rich woodland; dry foothills forest; montane dry woodland; montane moist forest; sub-alpine woodland; grassland; plains grassy woodland; valley grassy forest; herb-rich woodland; sub-alpine grassy woodland; montane grassy woodland; riverine grassy woodland; riparian forest; rainshadow woodland

Colours indicate possibility of Populus tremula infesting these areas.

In the non-coloured areas the plant is unlikely to establish as the climate, soil or landuse is not presently suitable.

map showing the potential distribution of aspen

Red= Very high	Orange = Medium
Yellow = High	Green = Likely

Impact

QUESTION	COMMENTS	RATING	CONFIDENCE
Social
1. Restrict human access?	Can form thickets, in a 20-30 year old stand primarily composed of suckers 2500-3700 stems per hectare have been recorded (Worrell 1995) Suckering habit means that when cleared it can quickly regrow and often leads to denser stands (Worrell 1995).	h	h
2. Reduce tourism?	There is no evidence for Aspen effecting tourism in Australia, it may have some impact but it is not known to what extent. Exotic tree species could alter aesthetics. Suckering habit may mean constant maintenance is required to keep an area open (Worrell 1995).	m	l
3. Injurious to people?	Salicyl alcohol and salicylaldehyde found in the bark of the tree has been reported to cause allergic contact dermatitis (Aalto-Korte et al 2005).	ml	h
4. Damage to cultural sites?	There is no evidence for Aspen effecting cultural sites and infrastructure in Australia, it may have some impact but it is not known to what extent. Exotic tree may alter aesthetics Suckering root system may cause some damage, however there is no evidence of Aspen damaging infrastructure in Europe	m	l
Abiotic
5. Impact flow?	There is no evidence for Aspen effecting water flow in Australia, it may have some impact but it is not known to what extent. Can occur in riparian zones.	m	l
6. Impact water quality?	There is no evidence for Aspen effecting water quality in Australia, it may have some impact but it is not known to what extent. Can occur in riparian zones. Like willows it is deciduous and could alter the dynamics of the food web.	m	l
7. Increase soil erosion?	Highly developed root system, in wet areas slow decay of the leaves forming humus can limit the lower strata to mosses, which may then be exposed to surface erosion (Worrell 1995).	ml	mh
8. Reduce biomass?	This is dependent on what habitat is invaded. Grassland, heath and woodland biomass may increase as it is a tree species. In other forests and some woodlands alteration of understorey may see a slight decrease in biomass, as it shades out some species (Worrell 1995). Therefore overall this could balance out.	ml	mh
9. Change fire regime?	Unknown to what extent Aspen could alter fire regimes in Australia. Responds well to fire, as mature trees can sucker and an ash bed can form ideal conditions for seedling establishment (Latva-Karjanmaa et al 2006; Worrell 1995) Alterations of biomass may have some impact upon fire frequency or intensity.	m	l
Community Habitat
10. Impact on composition (a) high value EVC	EVC= Lowland Forest (V); CMA= West Gippsland; Bioreg= Strzelecki Ranges; VH CLIMATE potential. Can dominate the canopy to sub-canopy and has been known to form pure stands of up to 2ha however this is a rare occurrence (Worrell 1995). Therefore major displacement could occur, but for the species to form a monoculture in the upper strata is viewed as unlikely.	mh	mh
(b) medium value EVC	EVC= Heathy Woodland (D); CMA= West Gippsland; Bioreg= Strzelecki Ranges; VH CLIMATE potential. Can dominate the canopy to sub-canopy and has been known to form pure stands of up to 2ha however this is a rare occurrence (Worrell 1995). Therefore major displacement could occur, but for the species to form a monoculture in the upper strata is viewed as unlikely.	mh	mh
(c) low value EVC	EVC= Heathy Woodland (LC); CMA= West Gippsland; Bioreg= Gippsland Plain; VH CLIMATE potential. Can dominate the canopy to sub-canopy and has been known to form pure stands of up to 2ha however this is a rare occurrence (Worrell 1995). Therefore major displacement could occur, but for the species to form a monoculture in the upper strata is viewed as unlikely.	mh	mh
11. Impact on structure?	Can dominate the canopy to sub-canopy and has been known to form pure stands of up to 2ha however this is a rare occurrence (Worrell 1995). May also alter the understorey composition by altering the levels of shading, also under particularly dense stands on wet sites in its native range, the slow decay of the heavy leaf fall has reduced the understorey to just mosses (Worrell 1995).	mh	h
12. Effect on threatened flora?	No evidence of this	mh	l
Fauna
13. Effect on threatened fauna?	No evidence of this, in its native range it is habitat for a number of threatened species (Worrell 1995).	mh	l
14. Effect on non-threatened fauna?	Alteration of habitat could impact on species. No evidence in Australia for this species at this stage.	m	l
15. Benefits fauna?	In its native range it has an associated fauna including 130 red listed species (Suominen et al 2003). Including various insect species and birds especially woodpeckers, would provide some habitat for Australian species (Worrell 1995).	mh	m
16. Injurious to fauna?	Guinea pigs have been found to react to the Salicyl alcohol and salicylaldehyde found in the bark of the tree (Aalto-Korte et al 2005).	ml	mh
Pest Animal
17. Food source to pests?	Browsed by deer and hares (Latva-Karjanmaa 2006; Worrell 1995).	ml	h
18. Provides harbor?	Thicket forming tree species likely to provide harbour for many different species, no evidence on this reported	m	l
Agriculture
19. Impact yield?	Viewed in many parts of its native range as a harvestable crop itself, can out compete some forestry species not widely used in Australia (Worrell 1995). Invasion of pasture through suckering would reduce the are of production, this however would take time and not occur over a significant area as the majority of suckers occur within 40m of the parent tree (Latva-Karjanmaa 2006).	l	mh
20. Impact quality?	No evidence of this	l	m
21. Affect land value?	No evidence of this	l	m
22. Change land use?	No evidence of this	l	m
23. Increase harvest costs?	No evidence of this	l	m
24. Disease host/vector?	A host of pine twist rust (Melampsora pinitorqua) which effects Scots Pine (Pinus sylvestris) (Mattila 2002). The rust has not however been reported in Australia nor is Scots pine a significant crop.	l	m

Invasive

QUESTION	COMMENTS	RATING	CONFIDENCE
Establishment
1. Germination requirements?	Weather conditions have been found to effect germination and for seedling establishment to occur they have specific requirements of the seed bed and moisture levels. Germination can occur under variable conditions and has not been found to be effected by temperature, however as seeds are unlikely to germinate two months after being released germination can only occur seasonally in correspondence with the flowering of the tree (Latva-Karjanmaa 2006; Latva-Karjanmaa et al 2003; Latva-Karjanmaa et al 2006; Worrell 1995).	mh	h
2. Establishment requirements?	Seedling survival is generally low, for seedlings to establish they require adequate moisture, a good seed bed such as an ash bed and little to no shading (Latva-Karjanmaa et al 2006; Worrell 1995).	ml	h
3. How much disturbance is required?	In its native range Aspen is viewed as a pioneer species. Reported in heath in Scotland it is believed that it could invade similar habitats if a disturbance such as fire creates an opening (Butcher 1961; Dolezal et al 2004; Latva-Karjanmaa 2006). As fire can be part of the natural disturbance regime of habitat such as heath even after a fire these habitats are considered healthy and undisturbed.	h	mh
Growth/Competitive
4. Life form?	Tree mat be reduced to a shrub under less favourable conditions (Worrell 1995). Other.	l	h
5. Allelopathic properties?	Not described as having allelopathic effects, however due to leaf fall Aspen may increase the pH of the soil (Worrell 1995).	l	m
6. Tolerates herb pressure?	In its native range it is reported in woodland associated with low grazing levels and dispersal into higher altitudes is believed to be prevent due to grazing by sheep and deer (Worrell 1995). This species has invaded pastures with suckers from nearby populations (Webb et al 1988). No biological control agents or significant insect pests have been reported, therefore once established browsing by species like moose, sheep or deer as in the northern hemisphere is not going to limit the trees capacity to reproduce only the ability for the progeny to establish.	mh	h
7. Normal growth rate?	Has rapid early growth, however compared with other poplar species it is considered slow growing (Worrell 1995). As poplar species are considered fast growing trees Aspen would still be considered a competitive tree species (Jouve, Hoffmann & Hausman 2004). Reported to have faster growth than Picea abies (Norway spruce) and birch, 35 yield old stand of birch yielded 100m3 ha-1 compared with 480m3 ha-1 for a 36 year old stand of aspen (Johansson 2003).	m	h
8. Stress tolerance to frost, drought, w/logg, sal. etc?	Able to accumulate heavy metals with only a reduction in growth (Hermle et al 2006; Unterbrunner et al 2006). Is one of the most persistent species under drought on the Hungarian steppe (Worrell 1995). Drought tolerant; produces as protein that is being researched to bioengineer drought tolerant tomatoes (Pelah, Shoseyov & Altman 1995). Tolerance to salinity; Occurs on costal cliffs and can tolerate salt spray (Worrell 1995). Found not to be effected by as much as 150 mM NaCl in the soil solution (Jouve, Hoffmann & Hausman 2004). Tolerant of periodic waterlogging, having a mechanism for root aeration through pressurized gas transport (Grosse et al 1992). In addition to this Aspen will grow if not very well in poorly drained peat and soils where the ground water is stagnant (Worrell 1995). Very frost hardy, reported growing within the artic circle (Worrell 1995). Fire can promote suckering and provide ideal conditions for seedling establishment (Dolezal et al 2004; Latva-Karjanmaa 2006; Latva-Karjanmaa et al 2006)	h	h
Reproduction
9. Reproductive system	Most commonly reproduces vegetatively through suckering, Aspen can and does produce fertile seed however this requires both male and female trees and poor germination and seedling survival means seedling establishment is relatively infrequent in the species native range (Worrell 1995).	h	h
10. Number of propagules produced?	One catkin can produce 2000 seeds and a tree can have 40,000 catkins (Latva-Karjanmaa et al 2003). Seed production varies annually (Latva-Karjanmaa 2006).	h	h
11. Propagule longevity?	Seed viability reduces rapidly (Worrell 1995). Little seed has been found to germinate after two months as alternating periods of wetting and drying rapidly decrease the seed viability (Latva-Karjanmaa 2006; Latva-Karjanmaa et al 2006). Seed may be able to be stored for a number of years (Worrell et al 1999). The roots of aspen as a vegetative propagule have been noted as being capable of persisting for many years with only a few shoots (Worrell 1995).	l	h
12. Reproductive period?	There is variation on the reported lifespan of this species, however the minimum reported time span is still fifty years (Worrell 1995).	h	h
13. Time to reproductive maturity?	Suckers can remain dependent on the parent tree for many years (Worrell 1995). Sexual reproduction usually begins after 30-40 years, however in more open environments it can be as early as 20 years and trees can start suckering at 10 years (Latva-Karjanmaa 2006).	l	mh
Dispersal
14. Number of mechanisms?	Has very light seeds that are dispersed by wind (Latva-Karjanmaa 2006)	h	mh
15. How far do they disperse?	Seeds are dispersed at least 400-500m (Latva-Karjanmaa 2006) Suckers may occur up to 40m from the parent tree (Latva-Karjanmaa 2006).	mh	mh

References

Aalto-Korte K., Valimaa J., Henriks-Eckerman M.L. & Jolanki R., 2005, Allergic contact dermatitis from salicyl alcohol and salicyladehyde in aspen bark (Populus tremula). Contact Dermatitis. 52: 93-95.

Butcher R.W., 1961, A New Illustrated British Flora. Part 1. Lycopodiaceae to Salicaceae. Leonard Hill Limited. London.

Clapham A.R., Tutin T.G. & Warburg E.F., 1952, Flora of the British Isles. Cambridge University Press.

Dolezal J., Ishii H., Vetrova V.P., Sumida A. & Hara T., 2004, Tree growth and competition in a Betula platyphylla – Larix cajanderi post – fire forest in central Kamchatka. Annals of Botany. 94: 333-343.

Grosse W., Frye J. & Lattermann S., 1992, Root aeration in wetland trees by pressurized gas transport. Tree Physiology. 10: 285-295.

Hermle S., Gunthardt-Goerg M.S. & Schulin R., 2006, Effects of metal-contaminated soil on the performance of young trees growing in model ecosystems under field conditions. Environmental Pollution. 144: 703-714.

Johansson T., 2003, Mixed stands in Nordic countries -- a challenge for the future. Biomass and Bioenergy. 24: 365-372.

Jouve L., Hoffmann L. & Hausman J.F., 2004, Polyamine, Carbohydrate, and Proline content changes during salt stress exposure of Aspen (Populus tremula L.): Involvement of oxidation and osmoregulation metabolism. Plant Biology. 6: 74-80.

Latva-Karjanmaa T., 2006, Reproduction and population structure in the European aspen. Academic dissertation. Department of Biological and Environmental sciences, University of Helsinki.

Latva-Karjanmaa T., Suvanto L., Leinonen K. & Rita H., 2003, Emergance and survival of Populus tremula seedlings under varying moisture conditions. Canadian Journal of Forest Research. 33: 2081-2088.

Latva-Karjanmaa T., Suvanto L., Leinonen K. & Rita H., 2006, Sexual reproduction of European aspen (Populus tremula L.) at prescribed burned site: the effects of moisture conditions. New Forests. 31: 545-558.

Mattila U., 2002, The risk of pine twisting rust damage in young Scots pines: a multilevel logit model approach. Forest Ecology and Management. 165: 151-161.

Pelah D., Shoseyov O. & Altman A., 1995, Characterization of BspA, a major boiling-stable, water-stress-responsive protein in aspen (Populus tremula). Tree Physiology. 15: 673-678.

Suominen O., Edenius L., Ericsson G. & de Dios V.R., 2003, Gastropod diversity in aspen stands in coastal northern Sweden. Forest Ecology and Management. 175: 403-412.

Unterbrunner R., Puschenreiter M., Sommer P., Wieshammer G., Tlustos P., Zuoan M. & Wenzel W.W., 2006, Heavy metal accumulation in trees growing on contaminated sites in Central Europe. Environmental Pollution. Article in Press. 1-8.

Webb C.J., Sykes W.R. & Garnock-Jones P.J., 1988, Flora of New Zealand, Vol 4, Botany Division, Department of Scientific & Industrial Research, New Zealand.

Worrell R., 1995, European aspen (Populus tremula L.): a review with particular reference to Scotland I. Distribution, ecology and genetic variation. Forestry. 68: 93-105.

Worrell R., Gordon A.G., Lee R.S. & McInroy A., 1999, Flowering and seed production of aspen in Scotland during a heavy seed year. Forestry. 72: 27-34.

Global present distribution data references

Australian National Herbarium (ANH) 2007, Australia’s Virtual Herbarium, Australian National Herbarium, Centre for Plant Diversity and Research, viewed 15 Feb 2007 , http://www.anbg.gov.au/avh/

Den virtuella floran (DVF) 2007, Naturhistoriska riksmuseet, viewed 15 Feb 2007, http://linnaeus.nrm.se/flora/

Department of Sustainability and Environment (DSE) 2006, Flora information system [CD-ROM], Biodiversity and Natural Resources Section, Viridans Pty Ltd, Bentleigh.

Global Biodiversity Information Facility (GBIF) 2007, Global biodiversity information facility: Prototype data portal, viewed 15 Feb 2007, http://www.gbif.org/

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